Hcl is used to remove MF4, Fe2O3 and part of FeO. The residue is dissolved by H2SO4-HF-H3PO4. Then, NH4Fe(SO4)2 is added to oxidate low-valence titanium and the standard solution of K2Cr2O7 is used to titrate Fe2+. The amount of total iron minus the amount of iron which has been removed, so that the amount of residue Fe2+ can be adjusted. This method has many advantages such as simplicity, rapidity repeatability.